Thermal energy systems incorporating heat exchangers typically comprise a primary loop, from which heat is supplied or removed, and a secondary loop, to or from which heat is transferred. The heat exchanger transfers heat between the primary and the secondary loop. A heat transfer fluid is circulated through the primary loop, supplying heat to, or removing heat from, the primary side of the heat exchanger. A secondary fluid to which heat is supplied or from which heat is removed flows through the secondary side of the heat exchanger. The primary and secondary sides of the heat exchanger typically have numerous small passageways in close association through which the fluids flow, which facilitate the transfer of thermal energy therebetween.
Modern heat exchangers are compact and offer high performance, i.e., high rates of heat transfer. High performance is usually achieved by making the passageways very small, and providing many of them. However, as the size of the passageways is reduced, they become more prone to fouling or complete blockage due to the accumulation of sediments, scale, and mineral deposits that may be present in the circulating fluid. Fouling of the heat exchanger leads to a substantial drop in performance of the system. Specific measures taken to minimize fouling include monitoring and control of the chemical composition of the fluids, frequent disassembly for cleaning of the flow passages, and oversizing of heat transfer surfaces and flow passages to ensure that they will have sufficient capacity even when operating at decreased effectiveness due to fouling. In the case of thermal systems for heating potable or process water, there is a high probability that mineral salts and other impurities may be present in the water. In such cases a potential for fouling of the heat exchanger exists if the exchanger is not routinely cleaned or flushed of accumulated matter. In many applications, such as residential and small commercial installations, monitoring of the chemical composition of the water, routine disassembly and cleaning of the heat exchanger, or oversizing are not practical due to the associated costs.